RDMA/siw: Use helper function to set sys_image_guid

Use the addrconf_addr_eui48() helper function to set the sys_image_guid,
Also make sure the GUID is valid EUI-64 identifier.

Link: https://lore.kernel.org/r/20211124102336.427637-1-kamalheib1@gmail.com


Signed-off-by: Kamal Heib <kamalheib1@gmail.com>
Acked-by: Bernard Metzler <bmt@zurich.ibm.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>